On a cold, damp evening in early to mid-April, dozens of volunteers will gather around ponds, marsh or bog wetlands and even drainage ditches across the state, listening for the "peep peeps," raspy "quacks" and low "snores" of the male frogs that have begun calling for mates at their breeding sites.

These frog enthusiasts will be taking part in Michigan's 13th annual frog and toad survey, which was initiated in 1996 by the Department of Natural Resources' Natural Heritage Program.

Although some of the volunteers are professional biologists and herpetologists, thousands of interested citizens, including entire school classrooms, have participated in the survey.

"The survey has been one of our most successful and largest public involvement efforts," said Lori Sargent, who has been the survey's coordinator from the beginning. Almost 500 routes were registered throughout the state within the first two years, she said.

Survey routes consist of 10 sites at which volunteers stop and listen for frogs and toads and record the species and an abundance index for each species on a data sheet. Surveys are conducted in the evening, when more amphibians are active. Each survey route is visited three times during the spring months during the breeding season.

The frog and toad survey is important because, over the past 30 years, scientists have been concerned about declines and/or population die-offs of several amphibian species worldwide. This concern was not only for the species themselves, but also for the ecosystems on which they depend.

Frogs and toads, like many other aquatic organisms are sensitive to changes in water quality and adjacent land-use practices, and their populations undoubtedly serve as an index to environmental quality.

"We're hoping that more site-specific research projects may be initiated in areas where declines become significant to determine the causes of those declines and to gain insight into ecosystem degradation," Sargent said, "but it may take several more years to establish firm trends based on these surveys."

The good news, at this point, is that most of Michigan's frog populations appear to be stable, unlike what has been reported in many other parts of the country.

"The abundant species, like the spring peeper, are staying abundant and the more rare species, such as the Blanchard's cricket frog, are staying rare," Sargent said. "Concerns are beginning to surface about mink frogs, which are found only in the Upper Peninsula and the Fowler's toad, which is found only in the western and some southern counties."

Michigan also is a participant in the national North American Amphibian Monitoring Program, which coordinates frog surveys nationwide and sets standards for survey protocols.

For example, it is known that natural fluctuations occur in amphibian populations, but the intervals of natural cycles have not been discovered. Many years of data are necessary to be able to distinguish these fluctuations from those caused by man-made factors such as impacts of pesticides or habitat losses.

Weather factors also play an important role in calling surveys and can affect the amount and the quality of the data in any one year.

Since the annual frog and toad survey began, data has been submitted from all 83 counties and more than 150 routes across the state have submitted data each year.

"These 150 routes have submitted data on each of their 10 sites for the first 12 years, so that results in more than 21,000 long-term data points," Sargent explained. "Our survey data has been recognized as an important monitoring tool for the environment and is being used in the 'State of Michigan's Environment' biennial reports.

With the annual help from frog enthusiasts across the state, the Natural Heritage Program plans to continue the Michigan Frog and Toad Survey indefinitely and hopes to maintain a consistent and knowledgeable volunteer workforce. These individuals are providing a wealth of information on the status of our frog and toad populations and, at the same time, are helping to monitor the quality of our environment.

The survey is supported by contributions to the Nongame Fish and Wildlife Trust Fund and through purchases of the Michigan Wildlife Conservation license plate.

Individuals can help this important project and many endangered species programs by purchasing a Wildlife Conservation license plate available through the Secretary of State's office or by sending a donation to the Nongame Wildlife Fund, P.O. Box 30180, Lansing, MI 48909. Donations also can be made online through the state of Michigan eStore at www.michigan.gov/estore.

For more information on the Michigan Frog and Toad Survey or to get information on other projects supported by the Nongame Fish and Wildlife Trust Fund, visit the DNR Web site at www.michigan.gov/dnr.